1. Field of the Invention
The present invention relates to a lighting unit equipped with a cooling means for cooling a light source, and an image formation apparatus having it.
2. Related Background Art
In a prior copying apparatus, a photosensitive body is charged uniformly by a charger, then exposed with image light according to an original image emitted from a light source. After passing the processes of development and transferring onto a recording material, developer is heated and fused onto the recording material by a heat fusing unit, and finally, a copy product is obtained. This kind of an apparatus is provided with a fan or a fanning or cooling means for air exhaust, because the charger generates ozone when charging the photosensitive body. To inhibit an abnormal temperature rise of the light source or prevent the heat fusing unit from raising the temperature inside of the apparatus abnormally, a heat exhaust fan is also incorporated in the apparatus.
When the main unit of the apparatus is energized, the fans are driven at a certain rotational speed. For a compact apparatus, in particular, a fan for air and heat exhaust is used to for the limited space. This kind of a fan is driven at a certain rotational speed all the time while the main unit is being energized.
A fluorescent lamp or other illumination lamp is characterized by the fact that the light amount varies with the bulb surface temperature. In the aforesaid prior apparatus, the illumination lamp is cooled by the fan which is driven after the start of energizing the main unit. This brings about such a disadvantage as to prolong the duration from the start of energizing the illumination lamp until the lamp emits a required amount of light (This is especially noticeable under a low-temperature environment). Therefore, supposing a copy operation is started before the required amount of light is obtained, the starting portion of an image may become abnormally dense.
Thus, using the aforesaid prior apparatus, to start an copy operation when an original illumination lamp emits a required amount of light and thereby obtain an satisfactory image, the startup time must be greatly extended. As a result, the copy operation becomes time-consuming.